1. Field of the Invention
The present invention relates generally to the field of catheters, and specifically to the field of cardiac catheters designed for mapping and ablation of selected portions of cardiac circuitry accessible through blood vessels which are contiguous with the heart.
2. Description of Related Art
Cardiac pacing typically begins with a depolarization impulse at the sinoatrial (SA) node, which spreads as an electrical wave from its location in the right atrium across to the left atrium and down toward the zone between the atrium and the ventricles. At that point, another impulse conducts through the atrioventricular (AV) node and to a common pathway, known as the bundle of His, between the right and left ventricles. As long as this basic system is intact, impulses are transmitted normally and cardiac rhythm is maintained.
The natural impulses may be interrupted by a variety of congenital or external causes. Cardiac arrythmias typically result from such disrupted cardiac pathways, and take the form of brachycardia, tachycardias, and the like. Each of these is potentially fatal. Historically, treatment for such conditions has included drugs, such as lidocaine, quinidine, procainamide, certain Beta blocking drugs, open heart surgery. The less traumatic procedure of using specialized catheters instead of the traumatic procedure of open heart surgery, has led to the evolution of cardiac catheter technology.
Cardiologists and cardiac surgeons have used selective ablation to treat certain rapid heart rhythms, such as accessory pathways of AV reciprocating tachycardia. Either cryoablation or catheter ablation was used to disrupt the electrical pathway in the heart by disrupting accessory pathways of atrioventricular reciprocating tachycardia.
Surgical ablation of the accessory pathway was used as a method for treating patients with Wolff-Parkinson-White syndrome for over twenty years. High-energy shocks delivered near the coronary sinus ostium was used to ablate posteroseptal pathways. Radiofrequency (RF) current was used to selectively ablate various accessory atrioventricular pathways to treat the Wolff-Parkinson-White syndrome by Jackman et al., (New Engl. J. Med. 1991; 324(23): 1605-1611).
Atrial fibrillation (AF) afflicts about 1.5-2 percent of the population. AF is characterized by irregular, often rapid heart beats due to uncoordinated electrical activity of atria. These cause strokes, hinting, dizziness, palpitations, shortness of breath, and reduction in amount of blood pumped out by the hear. The latter is particularly important in patients who have low ejection fraction due to prior heart attacks.
Existing medicinal treatment for AF is only partially effective at best. Recent studies have shown that there is a minimum of 1-2 percent per year risk of life-threatening proarrythmia. That is, the medicine that is supposed to treat the irregular heart beats itself is responsible for causing death due to life-threatening irregular cardiac rhythms. Thus, most physicians now believe that antiarrhythmic treatment is not advisable except under unusual circumstances.
Treatment of AF with anticoagulants reduces risk of strokes but does not abolish strokes. The ideal surgical treatment for AF results in the abolition of the three detrimental sequelae of the arrhythmia. That is, the procedure restores a regular ventricular rhythm, restores normal cardiac hemodynamics, and alleviate the patient's vulnerability to thromboembolism. (See Cox, et al., J. Thorac. Cardiovasc. Surg. 1991;101(4):569-583; and, Cox, J. Thorac. Cardiovasc. Surg. 1991;101(4):584-592) The surgical approach taught by that publication effectively treats atrial fibrillation by creating an "electrical maze" in the atrium. Atrial incisions are introduced to prevent atrial reentry and to allow sinus impulses to activate the entire myocardium. Current efforts toward finding an effective treatment for AF are centered around identifying the proper locations to cauterize in the heart so that results of the one surgical procedure known to cure the problem can be replicated in a cardiac catheterization laboratory.
Radiofrequency catheter ablation has also more recently been used for the treatment of human type 1 atrial flutter (Feld et al., Circulation 1992;86(4):1233-1240) and for the treatment of atrioventricular nodal reentrant tachycardia (Jackman et al., New Engl. J. Med. 1992;327(5):313-318). Transcatheter radiofrequency or direct current energy to treat multiple atrial arrhythmias has provided a definitive cure for many patients without the need for thoracotomy; however, consistent, successful RF ablation of ectopic atrial tachycardia has remained elusive. One author discloses a new, flexible, basket-shaped recording catheter to facilitate rapid, high resolution mapping. (Jenkins et al., JACC 1993;22(4):1105-1110)
Jackman et al. disclose a quadripolar catheter with a distance of 2 mm between electrodes, a large-tip electrode, and a deflectable curve was used for the ablation for treating AV node reentrant tachycardias. The catheter was inserted through a right femoral venous sheath, and the tip electrode was positioned at the site from which the largest, sharpest, and earliest activation of the atrial end of the slow pathway (A.sub.sp) potential was recorded during retrograde slow-pathway conduction or from which the largest, sharpest, and latest A.sub.sp potential was recorded during sinus rhythm. RF current (550 to 750 kHz) was delivered at 45 to 70 V between the catheter-tip electrode and an adhesive electrosurgical dispersive pad applied to the left posterior chest. Current was applied for 45 seconds or longer but was terminated immediately in the event of an increase in impedance or displacement of the catheter electrode.
A variety of catheters currently are available having at least two ring electrodes for bipolar stimulation and/or recording. A single pair of electrodes is sufficient for routine pacing or recording; simultaneous recording and stimulation or ablation typically requires two pairs. The catheter construction may be of the woven Dacron variety, such as those commercially available from Bard Electrophysiology (Billerica, Mass.) or of the extruded synthetic materials such as polyurethane. Commercially available catheters typically are flexible enough to form loops and bends as such are encountered in the vascular system. An optimal catheter has a combination of torque control and flexibility.
One difficulty in treating abnormal cardiac rhythms, is that the tissue causing the abnormal rhythm is located in the right atrium at or near the tricuspid ring. Unlike the procedure for ablating tissue surrounding the mitral valve annulus, a coronary sinus catheter readily provides crucial information regarding placement of the catheter. Unfortunately, no such structure is present at the right side of the heart, thus most devices cannot effectively be positioned and secured at the proper position long enough to map and ablate.
One commercially available catheter is the Webster.TM. deflectable halo catheter, available from Webster Laboratories, Baldwin Park, Calif. That catheter includes a catheter body that is coiled in its proximal portion to resemble a halo. Once the tip of the catheter is placed into the ostium of the coronary sinus, the radius of the halo can then be increased or decreased by adjusting an attached manual control device, either advancing or withdrawing the catheter or applying torque to the catheter to turn it to one side or another. The device includes a protective sleeve to maintain its shape during shipment and storage. The catheter is available in a variety of catheter tip configurations, depending on the size requirements of the patient. Accurate positioning of such catheters often is difficult since the catheters slide in and out of the coronary sinus and on the atrial endocardium.
Vascular sheaths may be used to position a catheter at a desired position. A commercially available vascular sheath, or catheter assembly, is the Fast-Cath.TM. Hemostasis Introducer Swartz.TM.SR series, from Daig Corporation, Minnetonka, Minn. That vascular sheath is designed for the introduction of electrophysiology catheters or other catheters where the varying curves and longer length of the sheath aid physician technique. The series includes several catheters having manual control over the deflection of the catheter tip position. The different sizes and configurations of the catheters are necessary due to the limited range of motion for the catheter tips imposed by the mechanics of the devices.
Catheters have been developed that have an internal lumen through which a control device is inserted for controlled rotation of the catheter tip in the horizontal plane during frontal plane fluoroscopy. These catheters primarily are used for atrial and ventricular mapping. However, the ability of these catheters to bend and rotate once inside the atrium or ventricle are limited, since a relatively stiff catheter is more easy to control remotely yet does not bend to accommodate the passageways as readily as does a more flexible catheter which is more difficult to control remotely.
Furthermore, current characteristics of ablation catheters make them difficult to position and keep on the right atrial AV ring. The tip often falls back into the ventricle, especially during the application of RF energy. One attempt to address this problem was presented by Avitall et al. (JACC 21 (2); 418A, Feb. 1993; U.S. Pat. No. 5,263,493). That disclosed catheter includes a small adjustable loop positioned at the most distal portion of the catheter ring. The catheter adapts to the shape of the tricuspid ring when opened and is capable of reducing/expanding its diameter under separate control. The small adjustable loop is anchored in the RV outflow while the other end rests on the annulus of the tricuspid valve and is anchored by the inferior vena cava.
Avitall et al. (Abstracts 661h Scien. Sess., 88(4)(2), Oct., 1993) also disclose a catheter having a pigtail shape which was set into the catheter tip at a 90.degree. angle to saddle the pigtail curve over the mitral leaflets and into the tissue groove located around the AV ring. Both of these Avitall et al. catheters attempt to address the problem of maintaining an accurate and consistent catheter positioning once the catheter is deployed at the desired location.
Thus, there remains a need for a cardiovascular catheter which embodies a combination of torque control and flexibility for use in selectively mapping electrical activity of the heart and for ablating portions of the atrium or ventriculum, and which will remain in position once deployed. There also remains a need for effectively treating AF, atrial flutter, AV node reentry tachycardia, and AV reciprocating tachycardia.